It is known to first open raw coffee beans by means of water or steam and then to extract the caffeine by means of an organic solvent. If the extraction is effected by means of a hydrocarbon halide, such as methylene chloride or trichloroethylene, the solvent must be removed as completely as possible, leaving only very small amounts of solvent which, according to the present state of medical knowledge, are harmless.
If acetic acid esters, for example, acetic acid ethyl ester (Cf., e.g., German Pat. No. 588,644), are used for the extraction, the roasted coffee produced from raw coffee beans decaffeinated according to this process has an aftertaste which cannot be removed even by intensive steaming of the decaffeinated raw coffee beans.
If ketones are used for the decaffeination (Cf., e.g., Swiss Pat. No. 100,167 and U.S. Pat. No. 1,629,512), the coffee beans have spots after being roasted. The content of water-soluble substances in the raw beans is reduced in an undesirable manner. Furthermore, particularly the low-boiling ketones (acetone, butanone-2) effect an extraction of water from the beans whereby the time required for decaffeination is considerably increased. Additionally, the taste of the roasted coffee differs from that of an untreated roasted coffee.